1. Field of the Invention
The present invention relates to a structure of a shadow mask in a cathode ray tube for color picture tube and color monitor, and more particularly, to a structure for preventing howling of a shadow mask in a cathode ray tube, in which bent parts are extended in a horizontal front-to-back direction along short side edges of a non-effective surface of a shadow mask, to enhance a rigidity of an edge portion of the shadow mask, that increases a natural frequency, for improving howling characteristics of the edge portion of the shadow mask.
2. Background of the Related Art
In general, the cathode ray tube has howling caused by disturbances, such as external impacts, and sound waves, which make the shadow mask fastened to a main frame to vibrate so as to impede an exact focusing of electron beams onto respective pixels through holes in the shadow mask, that deteriorates a picture quality. In order to minimize the howling, though various methods are suggested, such as modifying a structure of the main frame, changing a material or structure of a spring which support the main frame, or the like, there is a limitation in elimination of the howling caused by the vibration of the shadow mask coupled with a vibration of the main frame to the root.
FIG. 1 illustrates a side section of a related art assembly of a panel and a shadow mask, and FIG. 2 illustrates a detailed perspective view of an outer appearance of the shadow mask in FIG. 1, showing the panel 1, the spring 2, the main frame 3, and the shadow mask 5 fitted in the cathode ray tube. The panel 1 has a fluorescent material screen on an inside surface thereof, and the shadow mask 5 selects a color from the electron beams emitted from an electron gun, and focuses onto respective pixels on the fluorescent material screen. To do this, the shadow mask 5 has an effective surface 7 having a plurality of holes 6 for focusing the electron beams onto respective pixels, and non-effective surfaces 8 on outer sides of the effective surface 7. Edge parts of long sides of the shadow mask 5 are fastened to the main frame 3. The shadow mask 5 is tightened from the main frame 3, and in general the main frame 3 is supported on the panel 1, a front glass of the cathode ray tube, by four plate springs 2(left, right, top and bottom). Other than supporting the main frame 3, as the plate spring 2 is required to attenuate external vibration, the plate spring 2 is designed thin so as to have a rigidity very smaller than the main frame 3. If a tension to the shadow mask 5 is not enough, the howling is occurred caused by external vibration. In this instance, even if the shadow mask 5 vibrates in up and down directions by the external impact, though the howling at a central portion of the shadow mask 5 is not distinctive as incident angles of the electron beams are not great at the central portion, the howling at a peripheral portion of the shadow mask 5 is significant as incident angles of the electron beams are great at the peripheral portion. Therefore, as shown in FIG. 3A, for preventing the howling in the related art, there are springs 3xe2x80x3 fitted to left and right sides of sub-frames 3xe2x80x2, and damper wires 9 are connected to the left and right side springs, for restricting vibration of the shadow mask. However, the damper wires 9 on the effective surface 7 of the shadow mask block the electron beams, to show dark shadow across the screen, and increases cost. As an alternative to the spring fastening, as shown in FIG. 3B, clips 10 are fitted to the left and right outer portions of the effective surface 7 of the shadow mask 5, for reducing an amplitude and a time period of the vibration by friction occurred between the shadow mask 5 and the clips 10. However, this case has not so great effect of vibration attenuation, and the fitting process and formation of the clips increases cost.
Accordingly, the present invention is directed to a structure for preventing howling of a shadow mask in a cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a structure for preventing howling of a shadow mask in a cathode ray tube, which can improve howling caused by up and down vibration of a shadow mask even at side portions of the shadow mask.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the structure for preventing howling of a shadow mask in a cathode ray tube having a panel with a fluorescent material screen on an inside surface thereof, the shadow mask for selecting a color of electron beams emitted from an electron gun, and frames each fastened to a long side of the shadow mask to support the shadow mask on the panel through connecting means for applying a tension to the shadow mask in a vertical direction, wherein the shadow mask includes an effective surface having holes for selecting the color of the electron beams, non-effective surfaces which form no screen, and howling prevention members bent along short side edges of the non-effective surfaces in a horizontal front-to-back direction.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.